System for producing thermal power



2, 1955 K. HOFMANN 2,714,289

SYSTEM FOR PRODUCING THERMAL POWER Filed April 22. 1949 INVENTOR. KURT HOFMA NN.

ATTORNEY United States Patent SYSTEM FOR PRODUCING THERMAL POWER Kart Hofinann, Winterthur, Switzerland, assignor, by mesne assignments, to Kurt Hofmann, Chieming ueber Traunstein, Germany Application April 22, 1949, Serial No. 89,163 Claims priority, application Switzerland May 14, 1948 4 Claims. (Cl. 60-59) The present invention relates to an improved system for producing power from hot gases.

The conventional cycle followed for the production of power from hot gases comprises compression of the oper ating medium, preheating the compressed medium by heat exchange with the expanded operating medium (main heat exchange), heating the preheated and compressed medium to the maximum temperature in the cycle, expanding the medium for producing useful power and, as stated, utilizing the heat contained in the expanded medium for preheating the compressed medium. If the cycle is operated as a closed cycle, the expanded medium, i. e. the gases, are further cooled after the heat exchange step and subsequently recompressed.

The object of the present invention is to provide a system whereby the heat losses incurred by the cooling of the gases are reduced and the cycle efliciency is increased.

This object is achieved according to the invention by diverting at least one portion of the expanded gases before their compression is completed, individually, separately compressing the diverted portion or portions and combining them with the primary portion after compression of the latter.

As a rule, the diverted and separately compressed portion is combined with the primary portion during preheating of the latter.

Diversion of a portion of the gas may take place before completion of the cooling of the expanded gases. It may, however, be done after completion of the cooling and before the compression, and the diverted portion may be expanded and used for cooling the full stream of the expanded gases, then separately compressed and combined with the primary portion after compression thereof.

In a further modification of the process according to the invention, diversion takes place during compression F of the gases and the diverted portion of the gases is preheated by means of the expanded gases after theiruse in the first preheating step, whereupon the diverted portion is compressed and combined with the compressed primary portion.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself however and additional objects and advantages thereof will best be understood from the following description of embodiments MIC .. this compression, the temperature of the carbon dioxide thereof when read in conjunction with the accompanying drawing in which Figures 1 to 5 are diagrammatic illustrations of five modifications of systems according to the present invention.

The same numerals designate the same parts in all figures.

For carrying out the process, for example, carbon dioxide at a temperature of 25 C. may be used, for example in a condition corresponding to that characterized by the intersection of the isotherm 25 C. with the left limit curve, at a pressure of 65.6 kg. per cm and compressed to 200 kg. per cm in a compressor 13 (Fig. 1). During is raised to about 47 C. After the compression, the CO2 is preheated in a heat exchanger 25, 22 in a heat exchange step which will be described later and thereafter heated in a heater 8 to the highest temperature occurring in the cycle, for example, to 600 C. With this high pressure, highly superheated CO2, the power producing machine, for example a turbine 11, is operated. The expanded gases leaving the turbine are used in the heat exchange step mentioned above for preheating the compressed CO2 in the heat exchanger 25, 22. Instead of cooling all expanded gases leaving the heat exchanger before their recompression, according to the present invention, a portion of the gases, for example 40%, is diverted, for example, after leaving the heat exchanger and is compressed separately in a compressor 26. The diverted and separately compressed gases are reintroduced into the cycle, for example, by cornbining same with the primary portion after the latter has been cooled in a cooler 12 and compressed. The combined gases are then preheated in the heat exchanger 22, superheated in a heater 8, and expanded in the turbine, whereupon the cycle begins anew. In this case, the separately compressed diverted portion will be reintroduced into the main cycle during the preheating step by heat exchange.

The gas stream may be divided before reaching the heat exchanger 12 and the diverted portion separately compressed.

It is also possible to divide the gas stream during the cooling step instead of ahead of this step. This is shown in Fig. 2.

In another modification of the process which is shown in Fig. 3, cooling of the expanded operating medium is completed as in the conventional cycle in a cooler 12, whereby the medium may be in the gas phase, or partly liquid, or in the liquid phase, and diversion of a portion of the gas takes place ahead of the compression step. In this case, the remaining or primary portion of the stream is compressed by pump 13, preheated in a heat exchange step in heat exchangers and 98, superheated, expanded, etc., as in the conventional cycle, whereas the diverted portion of the medium is expanded in a turbine 93 and this cold expanded diverted portion is used in a cooler 194 for cooling the total stream of the medium, in the present case CO2, thereafter compressed in a compressor 9s and reintroduced into the main cycle in the manner set forth above.

A portion of the operating medium may be diverted before completion of the cooling step as shown in Fig. 4.

By taking heat out of the total circulating stream in the cooler 104 by means of the diverted and expanded portion, the latter absorbs heat, and this heat is reintroduced into the cycle and serves to reduce the total heat loss.

In a further modification of the invention (Fig. 5), diverting a portion of the operating medium, in the present case CO2, takes place during the compression step; i. e. after completion of the cooling step, the medium is compressed to a limited extent in low pressure compressor stages 13a and a portion, say 40%, is diverted. The remaining portion is compressed in high pressure compressor stages 13b to the highest pressure occurring in the cycle, preheated in a heater 8'7, 85, superheated in the heater 8, expanded in the turbine 11, etc., as previously described. The separated and partly compressed portion is preheated in a heat exchanger 89, compressed in a compressor 83, and combined with the compressed primary portion. Since the diverted portion is cooler than the fully compressed remaining portion, which is preheated in the heat exchanger 87, it is possible to utilize a portion of the heat of the total stream leaving the internal heat exchanger for preheating the diverted and only partly compressed gases. The result is that the heat content of the gases expanded in the turbine 11 is utilized in the heat exchanger 89 beyond the main heat exchanger or recuperator 85, 87 and is therefore utilizedmore fully. The supplemental use of the heat in the expanded gases constitutes the gain connected with this modification of the new system which gain is caused by the fact that less heat is wasted by the removal of heat from the total circulating medium.

In all described modifications of the system the energy producing expansion may be carried out in' stages, and the'medium may be reheated between the stages; also, compression of atleast one of the separated portions may be carried out in stages and heat may be removed from the medium between the stages and transferred to the cooling agent, i. e. removed from the cycle, or it may be used for preheating the compressed medium in the heat exchange process; further, the stream of the medium may be divided several times instead of once. In all cases, the percentage of reduction of the heat to be removed from the cycle is greater than the percentage of reduction of the heat to be supplied to the cycle.

I claim:

1. In the process for producing power from a hot gas wherein the operating medium is compressed, preheated by heat exchange between the expanded and the compressed medium, heated by external heat to the maximum temperature in the cycle, expanded for producing power, cooled by removal of heat from the expanded medium to the outside, and recompressed as at the beginning of the cycle; the steps of diverting a portion of the operating medium after it has been expanded to the lowest pressure in the cycle, after it has exchanged heat with the compressed medium, and before completion of its cooling by removal of heat to the outside, of separately compressing the diverted portion to the highest pressure in the cycle, and of reuniting the separately compressed portion withthe remaining portion of the medium after completion of the recompression of said remaining portion to the highest pressure in the cycle and before the medium is heated by external heat.

2. A thermal power plant in which a gaseous working medium circulates through a system of means forming a closed circuit having a high pressure and a low pressure portion and'comprising a first compressor for compressing the medium and having an outlet, an internal heat exchanger receiving compressed medium from said compressor, an external heat supply means for heating the working medium leaving said heat exchanger, a prime mover in which the working medium thus heated is allowed to expand whilst the prime mover delivers power externally, said high pressure portion of said circuit extending from said outlet to said prime mover, said heat exchanger being connected for medium flow with said prime mover and receiving expanded medium therefrom for transferring heat from the expanded medium to the compressed medium, and a cooler connected to said heat exchanger for receiving expanded working medium from said heat exchanger for removing heat externally of the circuit, said cooler being connected for medium flow to said compressor, said low pressure portion of said circuit extending from said prime mover to said outlet; conduit means" connecting said low pressure portion downstream of at least a portion of said internal heat exchanger and upstream of at least a portion of said cooler with said 4. high pressure portion for short-circuiting a portion of the stream of the circulating medium from said low pressure portion to said high pressure portion, and a second compressor interposed in said conduit means upstream of the point where said conduit means is connected with said high pressure portion.

3. In the process for producing power from a hot gas wherein the operating medium is compressed, preheated by heat exchange between the expanded and the compressed medium, heated by external heat to the maximum temperature in the cycle, expanded for producing power, cooled by removal of heat from the expanded medium to the outside, and recompressed as at the beginning of the cycle; the steps of diverting a portion of the expanded operating medium before completion of its recompression, of separately compressing the diverted portion, and of reuniting the separately compressed, diverted portion of the medium with the remaining portion of the medium during the preheating by heate'xch'ange phase of'the process and after completion' of the compression of said remining portion 4. A thermai'p'ow'er plant in which a gaseous working medium circulates through a system of means forming a closed circuit having a high pressure and a low pressure portion and comprising a first compressor for compressing the rne'dium'and having an outlet, an indirect heat exchanger receiving compressed medium from said compressor, and external'heat supply means for heating the Working medium l eaving said heat exchanger, a prime rr'rover'inwhich the working medium thus heated is allowed to expand whilst the prime mover delivers power externally, said high pressure portion of said circuit extendingfrom said outlet to said prime mover, said heat exchanger being connected for medium flow with said prime mover and reeciving expanded medium therefrom for transferring heat from the expanded medium to the compressed medium,- and a cooler connected to said heat exchanger" for receiving expanded working medium from said heat exchanger for removing heat externally of the circuit, saidcooler being connected for medium flow tosaid compressor, said low pressure portion of said circuit extending from said prime mover to said outlet; conduit means connecting said low pressure portion with said high pressure portion within said heat exchanger for short-circuiting a portion of the stream of the circulating medium." from said' low pressure portion to said high pressure portion, and asecond compressor interposed in said conduit means.

ReferericesCited inthe file of this patent UNITED STATES PATENTS 602,426 Chatwood Apr. 19, 1898 605,997 Casalonga June 21, 1898' 1,601,384 Vianello a Sept. 28, 1926 1,636,361 Gibson July 19, 1927 2,294,700 Stroehlen -a Sept. 1, 1942 2,303,159 Cross et a1. Nov. 24, 1942 2,341,490 Traupel Feb. 8", 1944' 2,370,949 Gais'berger Mar. 6, 1945 2,384,587 Badenhausen Sept. 11, 1 945 2,495,604 Salzmann Jan. 24, 1950 OTHER REFERENCES Thermodynamics by Lester C. Lichty, 2nd ed., 1948, McGraw-Hill Book Co., New York, page 158 (Fig. 85). 

